1. Field of the Invention
The present invention generally relates to a welding method for forming an oxide passivation film on a weld and a process apparatus, and more particularly relates to a welding method making it possible to form an oxide passivation film mainly made of a chromium oxide film on the surface of a weld simultaneously with welding.
2. Description of the Related Prior Art
The integration level and the performance of a semiconductor device have been improved, a semiconductor device fabricating apparatus meeting the requests has been requested, and efforts for creating a higher-vacuum and higher-cleanliness atmosphere have been made.
To create an ultrahigh-vacuum and very-high-cleanliness atmosphere, it is necessary to completely control the out-gas discharged from the apparatus or a gas feeding piping system. The inventors of the present invention completed an oxide passivation film treating method after long-time research and development, thereby making it is possible to form an oxide passivation film having corrosion resistance and a very small quantity of out-gas and mainly containing chromium oxide on the surface of a weld. As a result, they succeeded in creating an atmosphere containing only a very small quantity of out-gas discharged from the apparatus, which cannot be detected by an existing measuring instrument.
However, as the apparatus is further increased in size and further complicated, the necessity for connecting a pipe with the apparatus after forming an oxide passivation film has increased. A new problem occurs wherein the atmosphere is contaminated because a weld is not covered with an oxide passivation, film, gas is easily absorbed into or removed from the weld therefor. Therefore when the welded places are increased, the out-gas quantity discharged from the welds cannot be ignored.
Moreover, an apparatus and a piping system using a corrosive gas has a problem in that the weld corrodes and thereby contaminates the atmosphere.
To form an oxide passivation film on a large complicated apparatus and a piping system, an oxide passivation film forming apparatus is also complicated and the cost increases. Therefore, a welding method making it possible to form a passivation film simultaneously with welding was strongly requested.
One object of the present invention is to provide a welding method making it possible to form an oxide passivation film having corrosion resistance and discharging only a very small quantity of out-gas on and around a weld during the welding process.
Another object of the present invention is to provide a process apparatus requiring a very-high-cleanliness atmosphere.